SEP client not showing up and display as in workgroup

I created an image with SEP Client installed, I use this image to deploy to multiple PCs, this is a migration from Windows XP to Windows 7. Some clients after migrated to Windows 7 don't show up in SEPM console. They origianlly show as offline, I deleted them and they are not showing backup! I tried to redeploy the client and SEPM console found the client but shown it with a workgroup name instead of the PC name.

How do I make them all showing up in SEPM? Thanks.